Jon, definitely brute force protection. There is a way of how to recognize a legitimate proxy (like AOL, etc.).
BTW if anyone is interested, we are finishing up our own system -
http://www.passprotector.com which combines a member area protection with a member are management (adding/removing members, etc.). All the software has been tested for the last two months on all our sites (
http://everycent.com) with excellent results... I will save more info for the upcoming one-time announcement... ;)